Effects of calcium carbonate nano-particles on the properties of PVDF/nonwoven fabric flat-sheet composite membranes for direct contact membrane distillation

The polyvinylidene fluoride (PVDF) flat-sheet composite membranes were prepared for membrane distillation using hydrophilic polyester nonwoven fabric as a support and the mixture of LiCl and PEG as non-solvent additive through coating and wet phase inversion process. The effects of hydrophobic calcium carbonate nano-particles on membrane morphology, porosity, pore size, pore size distribution, hydrophobicity, thermal properties and permeability were investigated. The nano-particles optimized membrane structure, enlarged pore diameter, narrowed pore size distribution and improved membrane porosity to some extent. In addition, the nanoparticles could also enhance membrane surface roughness and contact angle while increasing the crystallinity degree of the prepared membranes. Nonetheless, the excess nano-particles addition would deteriorate membrane structure, reduce membrane porosity and decrease pore size. During the desalination process of 35 g/L sodium chloride solution, the maximum transmembrane permeate flux about 49.37 kg/m(2)h was obtained with the feed solution at 83 degrees C and the cold distillate water at 20.0 degrees C. Furthermore, the flat-sheet composite membrane exhibited satisfying performance stability compared with the membrane without nano-particles addition in the 300 h continuous desalination experiments, indicating that the prepared PVDF/nonwoven fabric flat-sheet composite membrane may be of great potential to be utilized in membrane distillation process for desalination. (C) 2014 Elsevier B.V. All rights reserved.